Method of vibration dampening by surface griding

ABSTRACT

The invention refers to a method of vibration damping in order to reduce vibrations of supports of slabs, for surface grinding. Individual supports, regularly arranged over the surface of a grinding table consist of hydraulic cylinders communicating with each other and lockable in reached final positions in contact with the slab. Between groups of cylinders valves are arranged for accommodating the number of active cylinders to the size of the slab on the table.

[111 3,908,318 1 51 Sept. 30, 1975 Wallin [5 METHOD OF VIBRATIONDAMPENING BY 3.136.528 6/1964 Eatough 248/356 X S ACE G G 3,285,01511/1966 Carnegie C131. 91/411 R UX 3.381581 5/1968 Carnegie 91/411 R X[75} Inventor: Sven-Herman Wallin, Djursholm,

Sweden [73] Assignce: Ambar Investment 1nc., Herrlibcrg.

Switzerland [22] Filed: Mar. 22, 1974 [211 App]. No.: 454,028

[52] U.S. C1 51/240 R; 269/20; 269/26; 269/266; 248/356; 60/581; 91/411R [51] Int. C1. B24B 41/06 [58] Field of Search 91/411 R; 92/146;248/20, 248/350, 356, 357, 354 H; 51/216 R, 240 R; 269/20, 26, 266, 267,311; 60/581 [56] References Cited UNITED STATES PATENTS 2,365,09512/1944 Miller ct a1. 137/101 Primuqv Ewminer-Edgar W. GeogheganAttorney, Agent, or Firnz-Fred Philpitt [57] ABSTRACT The inventionrefers to a method of vibration damping in order to reduce vibrations ofsupports of slabs. for surface grinding. individual supports, regularlyarranged over the surface of a grinding table consist of hydrauliccylinders communicating with each other and lockable in reached finalpositions in contact with the slab. Between groups of cylinders valvesare arranged for accommodating the number of active cylinders to thesize of the slab on the table.

4 Claims, 2 Drawing Figures US. Patent Sept. 30,1975 Sheet 2 of 23,908,318

2h AT 3 210% 2 METHOD OF VIBRATION DAMPENING BY SURFACE GRIDING thegrinding head is not only rather heavy but also changes its workingpoint. As the slabs to be ground in certain types of machines vary insize between 1.25 m X 5 m and 2 m X 8 m it is easily understood that thelinear distances between the points of support and the edges of the slabcan be rather great even if the supports are located, owing to the deadweight, to minimize the resilience bending i.e. the deflection of theslab (the so-called support functions of Bessel). Especially when thepressure of the grinding head has its working point at the edges of theslab or at a corner the system support slab has a low static stability,whe'refore the slab in the extremes can be tilting. Because of greatlinear distances between the points of support and between the supportsand the edges of the slab, the pliancy of the slab will permitconsiderable dynamic as well as static resilience bending possibilities.Especially in fettling as well as in other grinding operationsvibrations are generated that can easily cause sympathetic vibrations ofgreat amplitudes. As large and rather pliable parts of the slab arehanging freely on a few supports the vibration amplitudes can becomeconsiderable even if no sharp tuning is present as in the case forresonance vibrations. By surface grinding (fettling) (especially orrolling-mill slabs) it seems, in practice, to be extremely difficult toavoid these intense vibrations. There is one further circumstance thatseems to speak against a three point supporting, as this will causeconsiderable free overhang and deflection at the edges and at the middleof the slab, and that is the fact that the pressure of the grindingwheel, besides the dead weight of the slab will contribute to thedeflection, and will cause the grinding wheel partly to work on anascent and partly to work on a descent when grinding from one side tothe other. This greatly disturbs the grinding head control, which amongother things aims at maintaining a constant average depth of cut.

For the above reasons a three point support only cannot be accepted andat the present time normally several supports of equal height (oftenfour) are used in order to create, across the rectangular slab, a linearcontact with the slab. On the top of the supports there are bearingsurfaces for pads of wood or rubber. This method of positioning theslabs, however, gives a statically determined positioning only if thesupports are of exactly the same height and if the slab is absolutelyplane and infinitely rigid. None of these demands is fulfilled inproduction. If, therefore, the slabs are bent or warped the supportingpads will be differently loaded, and their elastical deformability willbe made use of for a load distribution between the different supportsand between the ends of the supports. This, however, means that theslab, owing to the at least relative to its point of action varyingforce at right angles to the slab due to the pressure of the grindingwheel, will obtain a resilience bending, the magnitude of which is alsodependent on how much the pads have already been compressed due to theload distribution. This is especially the case when rubber pads are usedbecause of their greater deformability than wood due to the fact thatthe flexibility of rubber is great for small deformations and decreasesat large and increasing rates of deformation to very smmall amounts.Certainly thick rubber pads can eliminate the need of, wooden padseither to alter the thickness of the pads or to wedge between the slabto obtain individual supports when the slabs are bent and warped, butthe varying force of support and the flexibility can normally not beeliminated. Very bent and warped slabs can require wood mounts under therubber pads or wedging at the edges. When the slab has been turnedupside down all support pads have to be re-arranged which takes costlytime. It should be pointed out that possible corrections of thethickness of the pads are done by an estimation of the crookedness ofthe slab.

The result of todays methods of supporting slabs is that the way ofsupport and the rigidness of the slab are very uncertain factors in theproduction contributing to extremely varying vibration conditions thatseem to be very apt to favour vibrations, giving rise to poor surfacesand being detrimental to the way of cutting of the grinding wheel andconsequently in the long run also being, detrimental to the human ear,to the grinding wheel spindle, to the electric motor and to the completegrinding machine. In particularly, measurements seem to show that theelectric motors are subject to vibration rates above 30 mm/sec, to becompared with standardized values of maximally 7.1 mm/sec.

From what has been stated above it is evident that matters need to betaken to create a better and more evenly distributed and less flexiblesupporting of slabs. One object of the present invention is to masterthe problems described above.

The present invention will be more readily understood from the followingdetailed description.

FIG. 1 illustrates an ordinary hydraulic cylinder with motion limitedplunger.

FIG. 2 is a drawing of a table for a grinding machine with a system ofcommunicating pressure cylinders.

The hydraulic cylinders utilized according to the invention are of atype known per se. They comprise a stationary cylindrical portion 30suitably provided with a broadened base aprt 31 to be secured to a tablebed 32. In the cylindrical portion 30 a plunger or piston 33 is movable,and sealing means 34 is provided at the gliding surface. Exchangeablesupport pads 35 are provided at the top of the piston which, for thisreason. suitably is hollow but is closed at its bottom end. Through aninlet and outlet opening 36 a suitable hydraulic medium 37 as oil cancommunicate with the interior of the cylindrical portion 30 below thepiston 33. In order to limit the motion of said piston in the downwarddirection a limiting ring 38 is arranged.

slab and withstand the maximum pressure of the grinding wheel, and afterpositioning the slab on the support pads of the pressure cylinders, thecylinders communicate hydraulically with each other in order to bringabout an accommodation of the position of the support pads to the formof the slab. When the slab finally rests on the support pads of thepresent cylinders and has been positioned in a macro-geometricallyhorizontal position, every single pressure cylinder is locked in itsposition by the means of valves that cut them out from the othercylinders in the system. The communication (opening and shutting)between the cylinders is performed by means of magnetically operatedvalves that by absence of current shut the flow of oil by means of aspring loaded valve slide. If the slab does not entirely cover the tablein the X and Y directions, see FIG, 2., manually or automatically row Acan be disconnected by the valve 2, rows A and B by the valve 3 and soon and row K can be disconnected by the valves 8 to 15, the row J by thevalves 16 to 23, and so on.

When the movable table is parked at one end automatically a multi poleplug 24 on the table will engage a resiliently fitted socket 25,bringing about contact actions for current supply and for the control ofthe valves.

In order that the support pads of the pressure cylinders shall not makeimpressions in the slab surface and to prevent sliding of metal to metalby great tangential components of the grinding force or by theacceleration or retardation of the table and to bring about a desiredvibration damping, the pressure cylinder support pads are provided witha shallow bowl form surface 35 for the mounting of wooden pads, rubberpads or pads of other energy absorbing material, see FIG. 1.

The elastic properties of these pads are depend upon material, thicknessand surface pressure (equal for all cylinders) wherefore a well adaptedand vibration damping deformation of the pads can be achieved thanks tothe energy absorbing properties of the material.

What is claimed is:

l. A levelling and vibration damping support system for a slab that isto be ground, said system being characterized by a. a horizontallydisposed table bed,

b. a plurality of upright hydraulic cylinders secured in a pattern ontop of said table bed so that the upper portions of said cylinders willsupport said slab,

c. a closed hydraulic communicating system interconnecting the hydrauliccylinders that are to support the slab,

d. a plurality of magnetically operated valves in said system forcontrolling the flow of hydraulic fluid to and from each hydrauliccylinder, and

e. means for activating or deactivating each of said magneticallyoperated valves,

whereby when a slab is placed upon said upper portions of said patternof hydraulic cylinders, all of said magnetically operated valves can beunlocked at once so as to equalize the pressure of the hydraulic fluidin each of said hydraulic cylinders and after the loading of the slab onsaid cylinders is accomplished and the grinding is to start, themagnetically operated valves can be locked so that there is no flow offluid between any of the hydraulic cylinders.

2. A system according to claim 1 in which the cylinders are arranged ina regular pattern of longitudinal and transverse rows with respect tothe table bed.

3. A system according to claim 2 in which rows of cylinders not coveredby a loading slab can be disconnected by said means for deactivatingsaid magnetically operated valves.

4. A system according to claim 1 in which the mag-,

netically operated valves are closed by the absence of a control currentused for their operation.

1. A levelling and vibration damping support system for a slab that isto be ground, said system being characterized by a. a horizontallydisposed table bed, b. a plurality of upright hydraulic cylinderssecured in a pattern on top of said table bed so that the upper portionsof said cylinders will support said slab, c. a closed hydrauliccommunicating system interconnecting the hydraulic cylinders that are tosupport the slab, d. a plurality of magnetically operated valves in saidsystem for controlling the flow of hydraulic fluid to and from eachhydraulic cylinder, and e. means for activating or deactivating each ofsaid magnetically operated valves, whereby when a slab is placed uponsaid upper portions of said pattern of hydraulic cylinders, all of saidmagnetically operated valves can be unlocked at once so as to equalizethe pressure of the hydraulic fluid in each of said hydraulic cylindersand after the loading of the slab on said cylinders is accomplished andthe grinding is to start, the magnetically operated valves can be lockedso that there is no flow of fluid between any of the hydrauliccylinders.
 2. A system according to claim 1 in which the cylinders arearranged in a regular pattern of longitudinal and transverse rows withrespect to the table bed.
 3. A system according to claim 2 in which rowsof cylinders not covered by a loading slab can be disconnected by saidmeans for deactivating said magnetically operated valves.
 4. A systemaccording to claim 1 in which the magnetically operated valves areclosed by the absence of a control current used for their operation.